UWM researchers trying to put more perch on your table
They are a favorite choice of the classic Wisconsin fish fry. They are also slow growers, finicky eaters and poor survivors.
Now, the University of Wisconsin-Milwaukee School of Freshwater Sciences is trying to bridge that inherent contradiction in perch.
The school is continuing to refine methods of aquaculture, or fish farming, to make it profitable. Aquaculture is likely the best option for getting more perch on dinner plates.
Further, the Fund for Lake Michigan has awarded $100,000 to the UWM Great Lakes Genomics Center — part of the Freshwater Sciences School — to sequence the DNA of perch and two other species. The idea is to develop ways to improve their health.
The research is not just academic. Wisconsin restaurants and wholesalers find themselves in competition due to the collapse of the perch population in Lake Michigan. The native fish has been declining since the early 1990s, most likely because of changes in the lake's food web brought on by invasive species.
Although the supply has been fairly good this year, it can still be tight from week to week, said J.P. Toske, the executive chef and operations manager at St. Paul Fish Company.
With no commercial fishing in Lake Michigan, Canadian suppliers are often the source now.
When algae blooms resulted in a poor perch harvest three years ago, Toske remembers his Canadian supplier instructing its delivery driver “not to let anyone see what was in the truck so that no one got jealous or upset about who was getting more,” he said, laughing.
Considering that 80% of American seafood is imported, aquaculture offers an opportunity to improve local economies. Additionally, the stringent regulations imposed on U.S. fish farmers result in a high-quality product; growth hormones are prohibited for fish and contaminants like lead and polychlorinated biphenyls (PCBs) are closely monitored.
That doesn't mean, however, that farming perch is easy.
A female perch lays 5,000-20,000 eggs, but numbers are the only factor that baby perch have on their side. A small yolk sack, their tiny size (about the length of a hyphen), minuscule mouths, and lackluster swimming ability leave them prone to starving. Only about 1% survive to adulthood.
“They’re really fragile. For the first 10 or 15 days, we can’t even touch them with a net. As soon as they touch a net they keel over and die,” said Osvaldo Jhonatan Sepulveda Villet, a professor at the School of Freshwater Sciences.
Villet and his colleagues have focused on indoor recirculating water systems rather than outdoor ponds because they offer more control over environmental conditions. The researchers have increased perch survival rates to more than 25% using recirculating systems.
Food for baby perch still presents a problem for commercialization.
Newly hatched perch can only fit tiny, live animals called zooplankton into their mouths, which complicates matters because cultivating zooplankton is unreliable. A commercial feed would be ideal, but no one has been able to make a pellet small enough to be successful.
Dong-Fang Deng, a senior scientist at the School of Freshwater Sciences, has focused her efforts on developing pellet feeds for older perch.
“How you manage the diet is very important,” Deng said. Farmed perch are generally fed formulas developed for trout or salmon, but different fish have different nutritional requirements. “Like if a human runs a marathon, you’ll need different nutrients,” she said.
The trout and salmon feeds result in fatty bellies and livers in perch, which hurts fish health and wastes nutrients (and money) by converting feed into fat instead of filets.
Deng also evaluates the effect of different nutrient sources. Perch are carnivores, and fishmeal has been the main protein used. Deng views fishmeal as an unsustainable resource since it comes from wild caught fish, and wants to convert perch into vegetarians by incorporating plant proteins like soy.
Interestingly, Deng’s work has shown that feeding behavior plays an important role in a food pellet’s success.
Perch must eat their food as soon as it enters the water to prevent nutrients from leaching. Some fish like food that floats on top of the water. Others prefer food that sinks to the bottom of the tank. However, perch only eat food that stays suspended in water. “They’re very picky,” said Deng.
Villet acknowledged that recirculating systems are more expensive to set up, but the increased productivity and control they offer can counterbalance the capital cost.
Through a combination of controlled environmental conditions and years of selective breeding for fast-growing fish, the School of Freshwater Sciences can raise perch to market size in less than 10 months rather than the 18 months needed for outdoor ponds.
Soon, Villet and Deng will have an additional tool to guide their efforts — the DNA sequencing.
Rebecca Klaper, a UW-Milwaukee professor and director of the Genomics Center, said that previous genome sequencing has focused predominantly on humans and a handful of organisms used as models for humans. Only cursory information is known about other species like perch.
Deng hopes the results will identify genes that she can use early in the perch life cycle to evaluate how her feed formulas affect their health. Being able to track variables other than growth could help speed up her work. The perch genome should also give Villet insight into perch populations that are good candidates for the aquaculture breeding program.
Moving forward, Villet is optimistic about the future of perch aquaculture. There is a lot of water, industrial space and people looking for high quality seafood in the Midwest, he said. “So why don’t we put those three things together and make a bigger industry for fish farming?”